This invention relates to high impact resistant thermoplastic compositions containing acrylonitrile-butadiene-styrene (ABS) resins.
Acrylonitrile-butadiene-styrene resins are well known thermoplastic polymers useful in a variety of applications where resin properties such as impact strength, ready moldability, tensile strength and modulus, hardness, stability, surface gloss of the finished article and the like are important. Numerous processes have been developed for preparation of such resins including emulsion, bulk, solution and suspension polymerization and a combination of these techniques. In all these processes which are all well known in the art, styrene and acrylonitrile are graft copolymerized onto a butadiene rubber backbone, such as a butadiene homopolymer or a rubbery copolymer of butadiene and another comonomer, e.g. styrene. The rubber content of the graft copolymer product generally ranges from about 4 to about 60 percent by weight and the weight ratio of polymerized styrene to polymerized acrylonitrile in the copolymer grafts is generally roughly about 3:1 although other ratios may be employed.
Resin compositions comprising physical blends of the aforementioned acrylonitrile-butadiene-styrene graft copolymers with styrene-acrylonitrile copolymers, (SAN) are also well known and have acquired wide commercial acceptance. The graft copolymer component is then usually one having a relatively high butadiene rubber content and inherently a high impact strength to offset the low impact strength of the styrene-acrylonitrile copolymer component.
A disadvantage of many ABS compositions is the relatively high cost of the graft copolymer. A major contributor thereto is the raw material cost of the polybutadiene or rubbery butadiene copolymer ingredient used in the polymerization reaction. Also, since the rubber must be chemically combined, i.e. grafted, to be effective, the morphology of the butadiene, particle size, particle size distribution, particle shape and degrees of grafting and internal crosslinking must be closely controlled, and such control adds substantially to the cost.
It is obvious from the above that less than adequate control of one or more of the aforementioned variables affecting the efficiency of the rubber would result in a product having less than optimum physical properties, such as lower impact strength.
Although it is known in the prior art that the impact strength of an ABS resin especially at low temperatures can be improved by blending it with a small proportion of mineral oil, the aforementioned disadvantages are usually not overcome since the improvement in impact strength thus obtained is generally accompanied by excessive and detrimental decreases in other properties such as tensile strength and hardness, which severly limits the amount of such impact enhancers to be incorporated in the blend for either cost reduction or upgrading purposes.
It is therefore an object of the present invention to provide a high impact ABS composition having a relatively low rubber concentration.
Another object of the invention is to provide an ABS composition of improved impact strength.
Still another object of the invention is to provide an ABS composition of high quality at reduced cost.
These and other objects will become apparent from the following detailed description of the invention.